In a future development, could the option of facial unlock plus PIN be considered? My thought is that if, perhaps due to shoulder surfing or telephoto lens, someone obtains your PIN then mugs you for the phone, they would not be able to unlock it with PIN only as your face is not in view. It would also mean that if an authority took your phone, you would need to be there at the time of access.
I already use PIN scramble, but I am wondering if security could be boosted further

No devices which are currently supported have Face Unlock, since the current implementation isn't secure enough.

That said, we plan to offer the option for a fingerprint + PIN unlock, which would help in shoulder surfing situations, along with situations where your finger can be forced onto the display (since one scenario requires your fingerprint, which a shoulder surfer won't have, and the other requires your PIN, which someone forcing your fingerprint onto the display may not have).